1. Field of the Invention
The present invention relates to a conductor layer, for example, formed in a magnetoresistive element, for example, for detecting an external magnetic field. Particularly, the present invention relates to a thin film conductor layer capable of preventing separation, a magnetoresistive element using the thin film conductor layer, and a method of producing a thin film conductor layer.
2. Description of the Related Art
Magnetoresistive elements include an AMR (anisotropic magnetoresistive) element utilizing anisotropic magnetoresistance, and a GMR (giant magnetoresistive) element utilizing a giant magnetoresistance. A high rate of resistance change can be obtained by a GMR element, as compared with an AMR element.
Of such GMR elements, a spin-valve type thin film element having a relatively simple structure and showing a change in resistance with a weak external magnetic field has the simplest structure comprising four layers including an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer and a free magnetic layer.
FIG. 9 is a sectional view of a conventional spin-valve type thin film element as viewed from the side opposite to a recording medium.
An under layer 6 is made of Ta or the like, and an antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic conductive layer 3, a free magnetic layer 4, and a protective layer 7 are deposited in turn on the under layer 6. As shown in FIG. 9, the antiferromagnetic layer 1 and the pinned magnetic layer 2 are formed in contact with each other, and the pinned magnetic layer 2 is pinned by an exchange coupling magnetic field generated in the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2, for example, in the Y direction shown in FIG. 9.
Referring to FIG. 9, hard magnetic bias layers 5 are formed on both sides of the laminate ranging from the under layer 6 to the protective layer 7 so that magnetization of the free magnetic layer 4 is arranged in the X direction shown in the drawing by a bias magnetic field from the hard magnetic bias layers 5.
Further, a main conductive layer 9 is formed on each of the hard magnetic bias layers 5 through an adhesive layer 8, and an adhesive layer (protective layer) 10 is formed on the main conductive layer 9. Hereinafter, the adhesive layers 8 and 10, and the main conductive layers 9 are sometimes referred to as the general term xe2x80x9cconductor layerxe2x80x9d. The adhesive layers 8 and 10 are made of, for example, Cr, W, Nb, or the like, and the main conductive layers 9 are made of xcex1-Ta, Au, Ag, Cu, or the like.
The layers of the above-described conventional spin-valve type thin film element are formed by sputtering or vapor deposition using an existing sputtering apparatus or the like. Particularly a DC magnetron sputtering apparatus exhibiting excellent thickness reproducibility is preferably used as the sputtering apparatus. The DC magnetron sputtering apparatus comprises a substrate and an electrode unit, which are arranged in the apparatus, and a magnet provided in the electrode unit. The electrode unit comprises a DC power source provided therein so that when the DC power source is operated, magnetron discharge is produced due to the relation between an electric field and a magnetic field to sputter a target provided on the electrode unit, to form a thin film (laminate) on the substrate opposite to the target.
However, deposition of the conductor layers of the spin-valve type thin film element by the DC magnetron sputtering apparatus has a problem in which tensile stress is applied to the conductor layers in the direction parallel to the film plane, causing separation of the conductor layers. Since tensile stress is applied to the conductor layers, it is difficult to increase the thickness of the conductor layers to a predetermined value.
Furthermore, in the conventional thin film element, the main conductor layers 9 are made of, for example, Au, Ag, or the like, which is a very soft metallic material. Therefore, when the surface opposite to a recording medium is scratched by dry etching after film deposition to exposure the structure of the spin-valve type thin film element shown in FIG. 9 to the outside, the main conductor layers 9 are sagged to cause a recess in the main conductor layers 9. The occurrence of such sagging undesirably causes, for example, a short-circuit.
The present invention has been achieved for solving the problems of the conventional element, and an object of the present invention is to provide a thin film conductor layer formed by applying compressive stress thereto for preventing separation of the conductor layer, a magnetoresistive element using the thin film conductor layer, and a method of producing a thin film conductor layer.
The present invention provides a conductor layer comprising a thin film made of a metallic material, wherein the crystal face spacing in the direction perpendicular to the film plane is larger than that of a bulk material made of the same metallic material as the conductor layer in the direction perpendicular to the film plane.
In the present invention, preferably, the metallic material comprises bcc-structure Cr, and the (110) spacing of the conductor layer in the direction perpendicular to the film plane thereof is 2.039 angstroms or more.
Also, an under layer is preferably formed below the thin film conductor layer, which is preferably made of xcex2-phase Ta having (002) face perpendicular to the film plane is.
The present invention also provides a magnetoresistive element comprising a laminate comprising an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer so that the direction of magnetization is pinned by an exchange coupling magnetic field with the antiferromagnetic layer, and a nonmagnetic conductive layer formed between the pinned magnetic layer and a free magnetic layer; and the thin film conductor layer formed on either side of the laminate.
The present invention further provides a magnetoresistive element comprising a laminate comprising a magnetoresistive layer and a soft magnetic layer which are laminated through a nonmagnetic layer, and the thin film conductor layer formed on either side of the laminate.
In the present invention, the thin film conductor layer is preferably exposed from a surface opposite to a recording medium.
The present invention further provides a method of producing a thin film conductor layer, comprising depositing the thin film conductor layer on a substrate in a DC magnetron sputtering apparatus with DC bias supplied to the substrate side.
In the present invention, the crystal face spacing of the thin film conductor layer in the direction perpendicular to the film plane thereof is adjusted by the voltage value of the DC bias.
In a conventional conductor layer (thin film conductor layer) formed in, for example, a magnetoresistive element, tensile stress is applied thereto, readily causing separation of the conductor layer. Therefore, in the present invention, the crystal face spacing of the conductor layer is appropriately adjusted to apply compression stress to the conductor layer.
As a result of examination of the relation between stress and the crystal face spacing of a metallic material used for a conductor layer in the direction perpendicular to the film plane thereof, the inventors found that the stress applied to the conductor layer changes from tensile stress to compression stress with increases in the crystal face spacing. Particularly, it was found from experiment that the crystal face spacing with which tensile stress is transferred to compression stress is the same as the crystal face spacing of a bulk material made of the metallic material in the direction perpendicular to the film plane thereof. In the present invention, therefore, the crystal face spacing of the conductor layer comprising a thin film in the direction perpendicular to the film plane thereof is not less than the crystal face spacing of a bulk material in the direction perpendicular to the film plane thereof.
Although, in a conventional element, a soft metallic material such as Au or the like is used for the main conductor layers 9 shown in FIG. 9, such a metallic material causes xe2x80x9csaggingxe2x80x9d when exposed from a surface opposite to a recording medium, thereby causing a danger of a short circuit. In the present invention, therefore, a hard metallic material such as Cr is preferably used in place of a soft metallic material such as Au, so that the danger of causing xe2x80x9csaggingxe2x80x9d can be prevented.
As a method of forming a conductor layer comprising a thin film in which the crystal face spacing in the direction perpendicular to the film plane is not less than the crystal face spacing of a bulk material, the crystal face spacing of the thin film conductor layer can be increased by applying a DC bias to the substrate side in the magnetron sputtering apparatus used.